1. Technical Field
The present invention relates to reproduction of a disc on which information is recorded, and more particularly to a technology for accessing to the first session lead-in of a multi-session disc.
2. Background Art
A compact disc (hereinafter referred to as CD) was formerly sold in form of medium on which music data being recorded. Recently, multi-session disc known as CD-EXTRA is being sold in form of medium on which computer-readable data (video data, etc.) is recorded as well as music data.
At the same time, general consumers often record desired data on recordable recording media, that is, Compact Disc Recordable (hereinafter referred to as CD-R). Data can be recorded on the CD-R in various formats. Typical recordable formats of CD-R include music CD format such as CD-DA (Compact Disc-Digital audio), and data format such as CD-ROM (Compact Disc Read-Only Memory). A system for recording data on a CD-R is called “CD-R system”, which is usually realized by providing a personal computer with a CD-R recorder.
In the initial stage of CD, mainly the music CD-DA format was employed, wherein the data was recorded by single-session multi-track system. FIG. 6 is a block diagram of conventional disc reproducing apparatus 60 for reproducing a music CD-DA disc. A reproducing unit 2 for reproducing data from a disc is loaded with a disc 1 to be reproduced, and includes a pickup and other mechanical units for reproducing the data of the loaded disc 1.
Data signal from reproducing unit 2 is demodulated in a signal processing unit 5, decoded into analog music signal in a D/A converter 10, amplified into a sufficiently large electric signal in an audio signal amplifier 11, and is output from a speaker 12. A control unit 4 controls the general operation of the disc reproducing apparatus. In disc 1, table-of-contents information (hereinafter referred to as TOC information) is recorded as index information. To control the general operation of disc reproducing apparatus 60, control unit 4 reads out the TOC information from signal processing unit 5 through a sub-code detecting unit 6, and stores in a TOC information storage unit 7. Control unit 4 fetches start time information of the track to be reproduced from the TOC information upon reproducing disc 1, moves an optical pickup to this position, and reads out the music data signal. These operations are executed on the basis of processing of the program stored in control unit 4. Operation of control unit 4 is realized by using a so-called microcomputer, and TOC information storage unit 7 is a so-called random access memory (RAM).
FIG. 7 shows a data layout example of a disc recorded in a single session. The disc region is roughly divided into a lead-in region LIN, a program region PGM, and a lead-out region LOT. The TOC information is recorded on lead-in region LIN at the inner peripheral side of the disc recorded in a single session.
Disc reproducing apparatus 60 (FIG. 6) first reads out the TOC information from disc 1, and displays the information about a certain track recorded on disc 1 in a display unit (not shown) such as liquid crystal display device, thereby urging the user to select a desired tune to be played. Therefore, when disc 1 is loaded into disc reproducing apparatus 60, in order to read the TOC information, disc reproducing apparatus 60 operates to move the pickup to lead-in region LIN.
For this operation, it is required that disc reproducing apparatus 60 recognizes the present pickup position. This operation is explained below.
FIG. 8 shows a structure of an expensive mechanism of conventional disc reproducing apparatus 60. In the expensive mechanism of FIG. 8, from one end of a spindle motor 81 for rotating a turntable (not shown) on which disc 1 is placed, an optical pickup traverse 82 is designed to move by electromagnetic interaction generated between a linear motor magnet unit 83 and a linear motor coil unit 85. In this mechanism, a slider 87 is coupled to optical pickup traverse 82, and when optical pickup traverse 82 moves, slider 87 of a potentiometer 86 also moves. Therefore, the position detection voltage corresponding to the position of optical pickup traverse 82 is obtained from a position detection voltage output terminal 88. Thus, in this reproducing apparatus, the pickup position is always recognized by using the potentiometer, and high speed control is realized by using the linear motor as the driving motor. However, the cost is raised by using the potentiometer and linear motor, and hence a simplified mechanism is employed in disc reproducing apparatus 60 (FIG. 6). This is an inexpensive mechanism. For example, FIG. 2 shows a structure of inexpensive mechanism.
In the inexpensive mechanism, the expensive potentiometer is not used for detecting the position of optical pickup 23. Instead, in the inexpensive mechanism, an inexpensive push switch for detecting position (innermost peripheral position detecting switch 20), which is turned on only when optical pickup traverse 22 is positioned nearly in the innermost periphery of disc 1, is employed. Innermost peripheral position detecting switch 20 is connected to control unit 4 (FIG. 6) as innermost peripheral position detecting unit 3 (FIG. 6). Further, in the inexpensive mechanism, instead of the expensive linear motor, a brush type DC motor without speed control mechanism of same type as used in a cheap plastic model is used as traverse motor 24.
Disc 1 is mounted on turntable 21 and driven by a spindle motor 25. Optical pickup 23 is built in optical pickup traverse 22. When traverse motor 24 rotates, a traverse feed gear shaft 26 rotates, and optical pickup traverse 22 is guided by a slide shaft 27, and moves in a very tight state.
Operation of disc reproducing apparatus 60 (FIG. 6) of inexpensive mechanism (FIG. 2) for reproducing a commercial music audio CD is explained below. The music audio CD is a recorded disc of CD-DA by aluminum vapor deposition in a single session. In the inexpensive mechanism, the position of optical pickup 23 cannot be always recognized. Therefore, when loaded with music audio CD (CD-DA), disc reproducing apparatus 60 operates in a procedure as shown in FIG. 9 and FIG. 10.
FIG. 9 and FIG. 10 are flowcharts showing operation of disc reproducing apparatus 60 (FIG. 6). Referring to FIG. 9, control unit 4 (FIG. 6) drives traverse motor 24 (FIG. 2) of inexpensive mechanism, and moves optical pickup traverse 22 (FIG. 2) in the direction of inner periphery (step 22). As a result, optical pickup traverse 22 (FIG. 2) is positioned on the almost innermost periphery of disc 1. When optical pickup traverse 23 (FIG. 2) is positioned on the almost innermost periphery of disc 1, innermost peripheral position detecting switch 20 is turned on, and it is detected (step 23). Consequently, control unit 4 (FIG. 6) stops traverse motor 24 (step 24), and sets the timer for determining the driving time of traverse timer 24 at 240 mS (step 26).
Referring next to FIG. 10, traverse motor 24 is driven in reverse direction (outer circumferential direction) (step 27). Judging whether surpassing the duration T of the timer (240 mS in this prior art) for determining the driving time of traverse motor 24 or not (step 28), traverse motor 24 continues to drive if not surpassing. If surpassing, traverse motor 24 is stopped (step 29). As a result, optical pickup 23 is moved at least to the outer circumferential position from the start position of lead-in LIN of disc 1.
Duration T is usually designed by selecting a value for moving to a considerably outer peripheral position from the start position of lead-in LIN, that is, in program region PGM. The reason is because a considerably safety allowance is needed from the aspect of fail-safe principle due to the following three causes. Of the three causes, (1) the ON position of innermost circumferential position detecting switch 20 varies depending on the mounting error (deviation of precision of screw fixing position) of innermost circumferential position detecting switch 20 on unit main body 28, or structural individual error of innermost circumferential position detecting switch 20, (2) the rotating speed varies due to fluctuation of supply voltage or individual difference of motor because brush type DC motor without speed control mechanism is used as traverse motor 24, and (3) the rotating speed is increased or decreased depending on ambient temperature. In conventional disc reproducing apparatus 60, the duration of T is set at T=240 mS so as to move to a position of about 3 minutes from end point of lead-in LIN at ordinary temperature by referring to sub-code information.
When optical pickup 23 is moved to position of about 3 minutes of sub-code information, it is required to access lead-in LIN in order to read TOC information next time. Herein, sub-code information is read again (step 30), and it is judged whether the present position is in lead-in region or not (step 31). The present position is in program region PGM, not in lead-in region, and hence the progress goes to No at step 31. Herein, 32 kicks are made in the direction of inner circumference (step 32). By repeating this process as many times as required, it is possible to access lead-in region LIN. Reaching within lead-in region LIN by detecting the sub-code, the pertinent TOC information is read (step 33), and it is judged if all necessary information is read or not (step 34). If judged to be Yes, reading of TOC information is completed, and the subsequent process is made, for example, part of TOC information is shown in the display unit (not shown) telling that three tunes are contained in the disc in total and that it takes about 55 minutes to reproduce them all.
Consequently, when the user manipulates reproduction by pressing, for example, PLAY key (not shown), the start position of the specified tune is acquired by referring to the TOC information, and by accessing this position, reproduction is started.
Disc reproducing apparatus 60 sometimes reproduced wrong data which is not originally a subject to be reproduced by mistake if the capacity of data stored in the first session is small in the case of reproduction of disc recorded in multiple sessions. The reason is that, owing to the small capacity of data stored in the first session, the access for reading the TOC information of the first session has surpassed the recorded portion of the first session to get into lead-in of another session. As a result, the TOC information of other session is read and stored. A radical reason of such malfunction is that most commercial music audio CDs are recorded in single session, not in multiple sessions, and other reason is that disc reproducing apparatus 60 is designed to reproduce single-session discs only.
Referring now to FIG. 3, it is more specifically described. FIG. 3 shows a layout of a disc recorded in multiple sessions. Each session of multiple sessions is composed of lead-in region, program region and lead-out region, and a multiplicity of such sessions are recorded on a disc 1. FIG. 3 also shows an example of data included in the TOC information recorded on multi-session disc 1. As specified in the standard, the lead-in region of multiple sessions (after the second session) is 60 seconds, the lead-out region of multiple sessions is 30 seconds, and the lead-out region LOT1 of the first session is 90 seconds. Therefore, if program region PGM1 of first session is extremely short, for example, 0 second, the start position of program region PGM2 of second session is understood to be an absolute address position at least 2 minutes and 30 seconds later.
The operation of disc reproducing apparatus 60 for reproducing a multi-session disc so-called CD-EXTRA recorded in multiple sessions are described as follows. CD-EXTRA has a data composition as shown in FIG. 3. In this explanation, a short CD-DA tune of 20 seconds is recorded in the first session, and CD-ROM data is recorded in a second session.
When such disc 1 is loaded, as already explained by referring to FIG. 9 and FIG. 10, by moving optical pickup 23 in the inner peripheral direction of disc 1, when optical pickup 23 is positioned nearly on the innermost periphery of disc 1, traverse motor 24 is once stopped. Then moving for 240 mS in the outer circumferential direction, optical pickup 23 is moved to position of about 3 minutes of sub-code. Next, to read TOC information, it is attempted to access lead-in LIN1 of the first session.
In this example, a short CD-DA tune of 20 seconds is recorded in the first session, and CD-ROM data is recorded in the second session, and therefore lead-in region LIN2 of second session is present at the position of about 3 minutes of sub-code. Therefore, since optical pickup 23 is already positioned at second session lead-in LIN2 of disc 1, the TOC information is read directly in this state without executing 32 kicks operation in the inner circumferential direction at step 32. However, what is read is the TOC information of second session lead-in LIN2. Therefore, the display device (not shown) shows the information of second session, that is, part of TOC information (for example, total number of tunes of 1, and total reproduction time of about 52 minutes).
When the user manipulates to start reproduction by pressing, for example, PLAY key (not shown), disc reproducing apparatus 60 starts reproduction by referring to the stored TOC information. In this case, however, instead of the intended first session music (CD-DA), reproduction of CD-ROM data in the second session is started.